Reversion to hyperhydration by addition of antibiotics to remove Pseudomonas in unhyperhydrated oregano tissue cultures

Hyperhydricity is a physiological malformation in tissue culture generated plants that impedes acclimation to outdoor conditions during plant regenera tion. Hyperhydrated plants are associated with low chlorophyll, low phenoli cs and high water content when compared to normal plants. In addition, hype rhydrated plants are morphologically characterized by translucent, enlarged , and brittle leaves and stems. Recently, a unique Pseudomonas sp. was used to prevent hyperhydricity in oregano shoot cultures. In this study three a ntibiotics, ampicillin, carbenicillin, and cefotaxime were tested to streng then the findings that prevention of hyperhydration is a direct result of i noculation with Pseudomonas, and therefore its removal would reintroduce hy perhydricity in the plants. To determine hyperhydricity the water content, total free phenolics, and chlorophyll levels of oregano shoot clones were c ompared. Furthermore, the growth, vigour and survival rate of these shoot c lones during regeneration in potted vermiculite were compared. Results show that water content and total free phenolics in antibiotic treated pre-inoc ulated clones reverted to levels present in hyperhydrated clones, while chl orophyll remained at the elevated levels found in untreated, pre-inoculated clones. The acclimation study showed that pre-inoculated clones not treate d with antibiotics had the greatest growth, vigour and survival rate of any treatment. (C) 1999 Elsevier Science Ltd. All rights reserved.